circle: Support two point circle construction

src/draw/shapes.typ

@@ -27,12 +27,16 @@
 /// circle((0,0))
 /// // Draws an ellipse
 /// circle((0,-2), radius: (0.75, 0.5))
+/// // Draws a circle at (0, 2) through point (1, 3)
+/// circle((0,2), (rel: (1,1)))
 /// ```
 ///
-/// - position (coordinate): The position to place the circle on.
+/// - ..points-style (coordinate, style): The position to place the circle on.
+///   If given two coordinates, the distance between them is used as radius.
+///   If given a single coordinate, the radius can be set via the `radius` (style)
+///   argument.
 /// - name (none,str):
 /// - anchor (none, str):
-/// - ..style (style):
 ///
 /// ### Styling
 /// *Root*: `circle`
@@ -42,20 +46,33 @@
 /// ### Anchors
 ///   Supports border and path anchors. The `"center"` anchor is the default.
 ///
-#let circle(position, name: none, anchor: none, ..style) = {
-  // No extra positional arguments from the style sink
-  assert.eq(
-    style.pos(),
-    (),
-    message: "Unexpected positional arguments: " + repr(style.pos()),
-  )
-  let style = style.named()
+#let circle(..points-style, name: none, anchor: none) = {
+  let style = points-style.named()
+  let points = points-style.pos()
+  assert(points.len() in (1, 2),
+    message: "circle expects one or two points, got " + repr(points))
+  assert(points.len() != 2 or "radius" not in style,
+    message: "unexpected radius for circle constructed by two points")
 
   (ctx => {
-    let (ctx, pos) = coordinate.resolve(ctx, position)
+    let (center, outer) = if points.len() == 1 {
+      (points.at(0), none)
+    } else {
+      points
+    }
+
+    let (ctx, center) = coordinate.resolve(ctx, center)
     let style = styles.resolve(ctx.style, merge: style, root: "circle")
-    let (rx, ry) = util.resolve-radius(style.radius).map(util.resolve-number.with(ctx))
-    let (cx, cy, cz) = pos
+
+    // If we got two points, use the second one to calculate
+    // the radius.
+    let (rx, ry) = if outer != none {
+      (ctx, outer) = coordinate.resolve(ctx, outer, update: false)
+      (vector.dist(center, outer),) * 2
+    } else {
+      util.resolve-radius(style.radius).map(util.resolve-number.with(ctx))
+    }
+    let (cx, cy, cz) = center
 
     let drawables = drawable.ellipse(
       cx, cy, cz,
@@ -65,7 +82,7 @@
     )
 
     let (transform, anchors) = anchor_.setup(
-      (_) => pos,
+      (_) => center,
       ("center",),
       default: "center",
       name: name,

tests/circle/test.typ

@@ -1,31 +1,28 @@
 #set page(width: auto, height: auto)
 #import "/src/lib.typ": *
+#import "/tests/helper.typ": *
 
-#box(stroke: 2pt + red, canvas(length: .5cm, {
-    import draw: *
+#test-case(radius => {
+  import draw: *
 
-    set-style(radius: (4, .5), stroke: none)
-    for r in range(0, 6) {
-      group({
-        translate((4.5, 4.5))
-        rotate(r * 30deg)
+  circle((0, 0), radius: radius, name: "c")
+  point("c.center", "M")
+}, args: (1, 1cm, (1, .5), (1cm, .5), (.5, 1), (.5, 1cm)))
 
-        circle((0,0), fill: (red, green, blue, yellow).at(calc.rem(r, 4)))
-      })
-    }
+#test-case(outer => {
+  import draw: *
 
-    set-style(radius: 0.45, stroke: black, fill: none)
-    for x in range(0, 10) {
-      for y in range(0, 10) {
-        circle((x, y))
-      }
-    }
-}))
+  let center = (1, 1)
+  circle(center, outer)
+  move-to(center)
+  point(outer, "O")
+  point(center, "M")
+}, args: ((2, 1), (rel: (1, 0)), (rel: (1, 1))))
 
-#box(stroke: 2pt + red, canvas(length: .5cm, {
+#test-case({
   import draw: *
 
-  for z in range(-2, 2) {
+  for z in range(-1, 2) {
     circle((0,0,z))
   }
-}))
+})

tests/helper.typ

@@ -1,5 +1,11 @@
 #import "/src/lib.typ" as cetz
 
+/// Draw a point + label
+#let point(pt, name) = {
+  cetz.draw.circle(pt, radius: .05cm, fill: black, stroke: none, name: "pt")
+  cetz.draw.content((rel: (.2cm, 0), to: "pt"), [#name], anchor: "west")
+}
+
 /// Draw a cross at position pt
 #let cross(pt, size: .25, ..style) = {
   import cetz.draw: *